1. Field of the Invention
The present invention relates to the processing of waste for disposal. In particular, the present invention relates to the encapsulation and immobilization of waste in glass using microwave energy.
2. Discussion of Background
The proper disposal of all kinds of wastes is an important issue. In particular, the disposal of hazardous wastes: biological, chemical and radioactive, is of particular concern to generators, regulatory officials and the public. These waste materials can present a hazard if they reenter the environment. Furthermore, there is the related issue of reduction of waste volume and minimization of disposal space.
A considerable quantity of such wastes are generated each year. Although progress has been made in reducing the volume of wastes generated and in recycling some components of the wastes, there remains a large volume of material that must be safely disposed of.
A number of techniques have been used in stabilizing and encapsulating hazardous wastes and the literature abounds with descriptions of these. A particularly effective technique, called vitrification, is the encapsulation of wastes in glass. Glass is very stable against chemical attack. Vitrification has been studied for decades in connection with radioactive wastes. Typically, the waste is slurried with glass frit into a glass melter where electrodes have heated the glass until it is molten. The waste is incorporated into the glass matrix in such a way that the final, cooled product will resist leaching of the waste for very long periods of time.
In other applications of vitrification, electrodes are placed directly in contaminated earth, which typically has a significant silicate component, and a voltage applied. The resistance of the ground results in sufficient joule heating to vitrify the waste in situ.
Heat can be applied to wastes in a number of different ways. Although the use of electrodes is well known for incorporating waste into glass, the use of microwave energy is known in treating halogenated hydrocarbons, as described in U.S. Pat. No. 4,935,114 issued to Varma. According to his process, he brings toxic wastes into contact with a bed of non-metallic, absorbing particles, such as activated carbon, then heats the waste to 500.degree.-600.degree. C. to destroy the wastes chemically.
However, there remains a need for methods for encapsulating and immobilizing a variety of wastes, methods that are simple and effective, methods that are flexible and reduce the volume of waste substantially from their pre-encapsulated form.